Gold-base alloy



Sept 22, i970 A. s. DARLING ETAL 3,529,95

GOLD-BASE ALLOY Filed July 14, 1966 2 Sheets-Sheet 1 pag.1.

A. s. DARLING ET AL 3,529,959

GOLD-BASE ALLOY sept. l22, 1970 Filed .July 14. 196e Sheets-Sheet 2 United States Patent Oce 3,529,959 Patented Sept. 22, 1970 3,529,959 GOLD-BASE ALLOY Alan S. Darling and Gordon L. Selman, London, England, assignors to Johnson, Matthey & Co., Limited, London, England, a British company Filed July 14, 1966, Ser. No. 565,276 Claims priority, application Great Britain, July 23, 1965, 31,556/ 65 Int. Cl. C2Zc 5 00,' D01d 3/00 U.S. Cl. 75--165 5 Claims ABSTRACT F THE DISCLOSURE A gold-base alloy which contains between 50% and 80% gold, between 0.04% and 0.5% iridium, and remaining part platinum, apart from the impurities. A method of making the alloy by induction melting the components, casting a sheet and homogenizing is also disclosed.

This invention relates to an improved alloy, more particularly, but not necessarily exclusively, intended for use in the manufacture of spinnerettes.

An alloy material suitable for use in the manufacture of spinnerettes should, as is well-known, desirably possess the following characteristics, namely: (l) uniformity 0f structures and behaviour, (2) small grain size, (3) resistance to attack by acids and alkalis and to abrasion. At the same time, the alloy should be capable of being subjected to a hardening treatment without dimensional changes taking place in the material treated.

Heretofore, spinnerettes have been made from a binary gold-platinum alloy, such, for example as a 70% Au and 30% Pt alloy. Such an alloy is mechanically strong and highly resistant to corrosion but has not proved entirely satisfactory for the purpose due to the fact that a tendency for the alloy to exhibit gross inverse segregation during casting renders it diiicult to Obtain a sufficiently uniform composition. Moreover, considerable grain growth is liable to occur when the` alloy is annealed.

With the aim of overcoming the aforesaid disadvantages, it has been the practice in recent years to add a minor amount of rhodium to a gold-platinum alloy, the most used alloy having substantially the composition 70% Au, 29.5% Pt plus 0.5% Rh. Such an alloy has been found to respond well to age-hardening.

More recently, however, it has been found that the ternary gold-platinum-rhodium alloy is open to criticism as a material for spinnerette manufacture on the ground that spinnerettes made from such an alloy are liable in use to serious corrosion, which has been attributed to the presence of massive particles of a hard second phase. It has been found, for example, that the presence of two contiguous zones of different phases may result in electrolytic corrosion particularly in the region of the outlet edges of the spinnerette holes, which could weaken the metal at these edges and cause parts thereof to be broken away.

Investigations have shown that this massive second phase is a hard platinum-rich phase in equilibrium with a gold-rich matrix, this platinum-rich phase apparently containing all the rhodium constituent of the alloy.

The Applicants have now found that the above disadvantages can be overcome in a simple manner and an improved gold-base platinum containing alloy which does not exhibit a massive platinum-rich second phase, can be readily obtained.

An object of this invention, therefore is to improve the properties of gold-base platinum-containing alloys.

Another object of the invention is to provide a goldbase platinum-containing alloy which offers greatly superior properties compared with known binary gpldplatinum alloys.

A further object of the invention is to provide an improved alloy for use in the manufacture of spinnerettes. With the above objects mainly in view, the invention contemplates the provision of a gold-base alloy which contains from 50% to 80% by weight of gold, 0.04% to 0.5% by weight of iridium and balance platinum apart from impurities.

In practice, it will be found that an alloy composed of 70 wt. percent gold, 29.8 wt. percent platinum and 0.2 wt. percent iridium is a particularly suitable alloy for use inthe manufacture of spinnerettes.

It has been found that by substituting iridium for the rhodium previously added to gold-platinum alloys, a very considerable degree of grain refinement is attained and there is a substantial absence of any objectionable platinum-rich hard second phase. If less than 0.04 wt. percent of iridium be included' in the alloy no significant grain refinement takes place, but no massive second phase regions are formed. If more than 0.5 wt. percent of iridium is added, considerable grain refinement is noticeable, but massive regions of a second phase are formed. It is advisable, therefore, to keep the iridium content within the range specified.

It appears that no particular conditions need to be adhered to in the manufacture of the improved' alloy, normal procedures being deemed sufficient. For example, the requisite proportions of the constituents of the alloy may be induction melted in an alumina crucible under argon and cast into a copper mould to yield a sheet ingot. This ingot is then homogenised for about 16 hours at a temperature of about 1000 C., followed by a period of about 48 hours at a temperature of about ll00 C. The alloy is then furnace cooled to 850 C. and water quenched, after which the alloy becomes ductile and can be cold rolled to sheet which is given a final anneal for a period of about 1/2 hour at a temperature of 1150 C., and water quenched.

Ternary gold-platinum-iridium alloys made in accordance with the invention `may be age-hardened similarly to the known gold-platinum-rhodium alloy.

As will be appreciated from the above, the improved alloy of the invention will be found to possess, to a greater degree than alloys hitherto available, the requirements of a satisfactory spinnerette alloy. The improved alloy has a uniform structure, any second' phase present being nely and evenly distributed through the goldplatinum matrix. The presence of iridium ensures an effective degree of grain refinement and the substantial absence of the aforesaid second phase will give a spinnerette made from this alloy a considerably longer life than has hitherto been attainable, and the corrosive action, above referred to, will not take place.

It is to be understood that the invention is intended to include within its scope any article, including spinnerette blanks and spinnerettes formed therefrom, which has been made from, or includes, an alloy embodying the invention.

In order that the invention and its advantages may be more clearly understood reference is now directed to the accompanying drawings in which;I

FIG. 1 illustrates a transverse section (X150) of an alloy containing 70% gold and 30% platinum in which the relatively coarse grain structure will be noted.

FIG. 2 illustrates a transverse section (X150) of an alloy containing 70% gold, 29.5% platinum and 0.5% rhodium and FIG. 3 illustrates a transverse section (X150) of an alloy containing 70% gold, 29.81% platinum and 0.2% iridium from which it will be noted that the iridium addi- 3 tive produces a significant grain refinement without showing any large quantities of a platinum rich phase. The grain refinement is clearly shown by a comparison of FIG. 4 (70% gold, 29.5% platinum and `0.5% rhodium) with FIG. 5 (70% gold, 29.8% platinum and 0.2% iridum), FIGS. 4 and 5 being comparable longitudinal sections. All the percentages given herein are by weight.

Although most of these new alloys can be effectively subjected to an age hardening process, it is not advisable to use this technique with alloys in accordance with the invention containing over 70% of gold.

What we claim is:

1. A gold-base alloy consisting essentially of from 50% to 80% by Weight of gold, from 0.04% to 0.5% by weight of iridium, and the balance platinum.

2. A gold-base alloy, according to claim 1, consisting essentially of 70% by weight of gold, 29.8% by weight of platinum, and 0.2% by weight of iridium.

3. A method of making a gold-base alloy which comprises melting 50% to 80% by weight of gold, 0.04% to 0.5 by weight of iridium and the balance platinum in an alumina crucible under argon, casting the alloy thereby formed into a copper mold to yield a sheet ingot, homogenizing said ingot by heat treatment for a first period of about 16 hours at about 1000 C. followed by a second period of about 48 hours at about 1100 C., furnace cooling the heated alloy to about 850 C., water quenching said cooled alloy whereby the alloy becomes ductile and then cold-rolling said alloy into sheet.

CII

4 4. A method as claimed in claim 3 wherein the sheet is subsequently annealed for a period of about `1/2 hour at a temperature of 1150 C. and is then water quenched.

5. A spinnerette made from the alloy claimed in claim 1.

References Cited UNITED STATES PATENTS 2,216,495 10/1940 Loebich 75-165 1,680,598 8/1928 Dreaper 75-165 2,143,217 l/l939 Truthe et al. 75--172 FOREIGN PATENTS 691,061 5 1940 Germany. 221,272 8/ 1942 Switzerland.

OTHER REFERENCES Gold Platinum Alloys, Darling, Platinum Metals Review, vol. 6, No. 3, July 1962, pp. 108-111.

Metallurgical Abstracts, vol. 26, 1959, p. 764.

Gold-Platinum Alloys, A. S. Darling, Platinum Metals Review, v01. 6, No. 3, July 1962, relied on pages 106 and 107.

CHARLES N. LOVELL, Primary Examiner U.S. Cl. X.R. 

